Penentuan pH dan suhu optimum aktivitas kitinase Bacillus cereus I.5 dan pengujian kitinase dalam mendegradasi eksoskeleton kutu bertepung putih (Ferrisia virgata Cockerell)

Abstract

Bacillus cereus I.5 is one of chitinolytic bacteria isolated from chilli rhizosphere. The chitinase could be apply as a biocontrol of plant pest. One method to precipitate enzyme by using ammonium sulphate. It could increase specific activity enzyme. This research was conducted to determine optimum pH and temperature of chitinase activity of Bacillus cereus I.5 and tested its ability to degrade chitin exoskeleton of Ferrisia virgata Cockerell, one of Jatropha’s pest. Enzyme activity was obtained at the 10% ammonium sulphate saturation level, which is 20 times higher compared to crude enzyme. Specific enzyme activity increased from 0,039 U/mg of crude extract to 0,778 U/mg after ammonium sulphate precipitation. Chitinase of B. cereus i.5 showed highest activity at pH 7,0 and 55 °C although the enzyme also showed its activity at pH 5,0-9,0 and temperature 26-≤55 oC. Application of crude chitinase and the enzyme after ammonium sulphate precipitation on degrading of chitin Ferrisia virgata showed it worked better if incubated firstly at its optimum temperature.